The invention concerns track drive devices intended in particular for the propulsion of all-terrain vehicles such as agricultural, vineyard and oyster-farming machines or civil engineering and forestry machines.
The invention concerns more particularly a track drive device of the type comprising at least one track formed from an endless flexible belt fitted on the inside with at least one row of studs located in the longitudinal direction of the belt, spaced at a constant distance apart and each delimited by two transverse faces in the transverse direction of the endless belt and by two lateral faces in the longitudinal direction of the endless belt, and two main wheels and support wheels on which the endless belt rolls.
In its patent FR-A-2 711 959 (93 13211), the applicant proposed a drive device of this type in which each stud was approximately shaped as a pyramid, at the base of which was defined at least one rolling slope. The lateral and transverse faces of the stud are flat and form an angle of between 8xc2x0 and 20xc2x0 for the lateral faces and between 30xc2x0 and 40xc2x0 for the transverse faces respectively in relation to a plane normal to the endless belt of the track.
In its patent FR-A-2 768 387 (97 11398), the applicant proposed a track drive device of the said type comprising particularly advantageous arrangements concerning in particular the main wheels and the support wheels on which the endless belt rolls.
In a track drive device of the said type, the main wheels normally comprise a posterior drive wheel and an anterior non-drive wheel.
Most often the non-drive wheel placed at the rear also serves as a track tensioning wheel and is borne by an oscillating beam which generally carries the support wheels placed between the anterior wheel and posterior wheel.
The drive wheel usually has, close to its median plane and perpendicular to its axis of rotation, a drive zone forming a drive gear for the track studs. This drive zone is generally formed by catches regularly spaced on the wheel periphery intended to enmesh in the empty spaces between the studs. These studs have a selected form facilitating the engagement and disengagement during their meshing with or release from the drive wheel.
Drive devices of this type are intended for use on vehicles which may be required to work in particularly difficult conditions, in particular on undulating terrain.
In extreme conditions, for example when working on steep gradients and cambers, the track may be subjected to considerable lateral forces tending to dislodge the track in particular from the posterior drive wheel but also from the anterior non-drive wheel.
The applicant has consequently considered the problem of improving the guidance and stabilization of the endless belt in particular in the region close to a main wheel.
To this end he proposes a track drive device of the type defined in the introduction which also comprises a guidance element placed between a main wheel and an adjacent support wheel and comprising rollers able to frame the lateral faces of the studs in order to ensure guidance and stabilization of the endless belt in the region of the guidance element.
This guidance element which can also be called a xe2x80x9cstabilizer elementxe2x80x9d therefore lies in the free space between a main wheel and the support wheel immediately adjacent to this.
Because this guidance element comprises rollers which frame the lateral faces of the studs, the result is an improvement in guidance of the endless belt in the region between this main wheel and this adjacent guide wheel.
Consequently even under extreme conditions, the track remains perfectly guided and stabilized and does not risk being dislodged from the main wheel and distorted.
In an embodiment of the invention, the guide element is placed between a main drive wheel and an adjacent support wheel.
In another embodiment of the invention, the guide element is placed between a non-driven main wheel and an adjacent support wheel.
The invention applies in particular to a device in which one of the main wheels and the support wheels are borne by an oscillating beam mounted pivotally about a shaft. In this case it is advantageous for the guidance element to be firmly attached to the said beam and thus be carried directly or indirectly by the beam.
The invention also applies to the particular case where the support wheels are grouped in pairs, each pair of wheels being borne on a rocker articulated on the oscillating beam.
In such cases it is advantageous for the guidance element to be borne by the rocker.
The guidance element can be located at an end of the oscillating beam which is close to the articulation shaft or at an end of the oscillating beam which is remote from the articulation shaft.
Naturally it is possible for the guidance element to be borne in another way for example directly by the framework supporting the track drive device.
In a preferred embodiment the control element comprises two coaxial rollers mounted loosely about a shaft and spaced apart.
These rollers preferably have their respective heads located in opposition, each able to rest against the two lateral faces of the studs.
According to another characteristic of the invention the heads of the rollers are shaped as a function of the shape of the lateral faces of the studs.
Thus it is advantageous for the heads of the rollers to have in general a truncated form and each be connected to a cylindrical skirt.
When the side faces of the studs are generally flat, forming an acute angle in relation to a plane normal to the endless belt, it is advantageous that the truncated parts of the roller heads form a less acute angle so as to promote contact of the rollers with the lateral faces of the studs in a region close to the endless belt at the base of the studs.
In other words this allows a greater play between the head of the stud and the roller than between the base of the stud and the roller.
In an embodiment of the invention, the rollers are mounted on two coaxial pivots borne by two arms respectively of a bracket.